Re: [PATCH] use UUID to map system devices to grub devices

[Robert Millan]

On Sat, Aug 08, 2009 at 07:13:20AM +0200, Felix Zielcke wrote:
> Am Freitag, den 07.08.2009, 21:22 +0200 schrieb Robert Millan:
> > On Fri, Aug 07, 2009 at 04:29:00PM +0200, Felix Zielcke wrote:
> > > Am Freitag, den 07.08.2009, 13:27 +0200 schrieb Robert Millan:
> > > > On Wed, Aug 05, 2009 at 08:18:29AM +0200, Felix Zielcke wrote:
> > > > > Am Dienstag, den 04.08.2009, 23:19 +0200 schrieb Robert Millan:
> > > > > > On Fri, Jul 31, 2009 at 06:26:51PM +0200, Felix Zielcke wrote:
> > > > > > > 
> > > > > > > If we'd do an arbitrary mapping then `grub-probe -t drive' would 
> > > > > > > show
> > > > > > > the wrong grub device.
> > > > > > > But except from this I think that would be okay.
> > > > > > 
> > > > > > We can never garantee that `grub-probe -t drive' will show the 
> > > > > > "right" drive,
> > > > > > at least on i386-pc, because we don't know how is BIOS going to 
> > > > > > order them.
> > > > > 
> > > > > Yes drive not, but the partition.
> > > > 
> > > > It's true, but we don't really make the distinction.  UUID search will 
> > > > find
> > > > a filesystem, which is in a partition (usually), and doesn't rely on 
> > > > partitions
> > > > being reliable.
> > > > 
> > > > That's fortunate!  It means we don't have to commit to partition 
> > > > numbers being
> > > > reliable, even if they are right now.
> > > > 
> > > > Because of this (unless I missed something), at the end of the day the
> > > > unreliability issue you described doesn't translate into any real 
> > > > problem
> > > > for us.  It just adds more to a problem we already solved.
> > > > 
> > > > > Unfortunately we don't have UUID support on every filesystem we 
> > > > > support
> > > > > like JFS. But I think it's not that commonly used.
> > > > 
> > > > Adding UUID support to new filesystems is very easy.  I did the first 
> > > > ones
> > > > with just 5-10 minutes of research and a few lines of coding.
> > > > 
> > > > Would you like to do JFS ?
> > > 
> > > I did it now for JFS.
> > > 
> > > I tried it now out with dos_part set to p + 2 with my find_by_uuid patch
> > > and now I get a `no such partition' error on my dmraid device.
> > > So we can't use an arbitary mapping in grub_util_biosdisk_get_grub_dev
> > 
> > Why not?
> 
> well then we would need to change the partition table parsing code to
> use the same arbitary mapping for GRUB_UTIL && LINUX then
> grub_util_biosdisk_get_grub_dev and I think that's not really a proper
> solution.

Why?  In that specific situation, it seems:

  - We're unable to obtain partition numbers reliably

  - It doesn't matter, because the upper layer will sort that out

Though, it'd be much better if we could obtain this information from Linux.
Did you figure out if the behaviour of that ioctl is a bug or is intentional?

-- 
Robert Millan

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